Commutator short-circuiting device for electric motors



g 13, 1929- E. c. BALLMAN 1,724,547

COMMUTATOR SHORT CIRCUITING DEVICE FOR ELECTRIC MOTORS Filed Feb. 12, 1926 [ow/1v C. BALL/1A Patented Aug. 13, 1929.

"UNITED STATES EDWIN C. BALLMAN, OF ST. LOUIS, MISSOURI.

COMMUTATOR' SHOBT-CIRCUITING DEVICF FOR ELECTRIC MOTORS.

Application filed February 12, 1926. Serial No. 87,809.

most of such devices a series of contactors 1s provided arranged so as to be movable under the centrifugal force of rotation so as to contact with the commutator bars in order to short circuit the same. Such dell. vices ordinarily provide for making butt contact between the contactors and the commutator bars. Since the armature currents in the rotor at the instant that the short circuiting operation takes place are usually 1 quite heavy, the short circuiting contact is frequently accompanied by more or'less arcing. This tends to heat the contact points of both commutator and contactor to such a degree that welding of the two together often takes place. In any case, the arcing causes pitting or corrosion of the contacting surfaces. Such corrosion naturally roughens the surfaces soas to cause poor contact and consequent uncertainty in the operation of the device.

One of the objects of this invention, therefore, is to provide a short circuiting device adapted to make and break the contact at one point thereof but to shift its contact point so as to provide for maintaining the short circuit through a different oint of contact from that at which the circuit is made and broken.

'Another object is to provide such a device in which the contactors will make rolling contact with the commutator.

Another great difiiculty met with in this type of machine is that the action of the short circuiting device at the predetermined 45. speed of the motor is often sluggish and,

therefore, uncertain not only. in its contact ing action but also in the critical speed at which it operates.

Another object of this invention, therefore, is to provide a short circuiting device which will operate with a quick and definite snap action at the proper speed.

Another object is to so proportion the parts of such a device so that the forces act- 5 ing thereon to cause its operation are increased as soon as such action begins, thereby causing quick and reliable action.

Further objects will appear from the following description taken in connection with the accompanying drawings, in which:

Figure 1 is a sectional view of part of the armature of a commutator motor equipped with a short circuiting device embodying this invention.

Figures 2, 3 and 4 are somewhat enlarged details of Figure 1 showing successive stages 1n the action of the device, and

Figures 5, 6, and 7 are views similar to Figures 2, 3 and 4 but illustrating another embodiment of this invention.

Referring now to the accompanying drawing, 1 designates the motor shaft, 2 the armature core and 3 the commutator connected to the winding 4.

A series of contactors 5 of copper or other suitable material is peripherally arranged about the shaft 1 and facing the radial face 6 of the commutator 3. The contactors 5 may be made by punching the same from flat or bevelled strip copper in a manner well known to those skilled in the art so that further description thereof will be unnecessary. These contactors may be arranged on a support or retainer 7 which has an outer flange adapted to engage the outer radial edges of the contactors, and an inner flange 8 adapted to be engaged by a pressure spring 9 surrounding the shaft 1. The pressure of the spring 9 acting through the retainer 7 forces the contactors against the face of the commutator hub 10 under normal conditions whenthe motor is not running. The outer flange of the retainer 7 may be equipped at intervals therearound with axially extending lips or fins 11 which extend between the contactors 5 and serve to retain them in the radial positions.

The contactors are of special shape. Each is formed with a weighted portion 12, a pivot portion 13 and a. contact face 14. Between the .pivot portion 13 and the con tact face 14a recess 15 is provided separating the pivot and the contact portions. The entire device is enclosed by a hood or cap 16 against the interior of which the spring 9 is adapted to bear and which is held in place on the shaft 1 by a key ring 17, seated in a groove 18 in said shaft. The cap 16 being of metal is spaced from the commutator 3 so as to avoid electrical cont-act therewith.

The space between the cap and the commu tator may be closed by a ring 19 of insulating material held in place by a head 20. on the cap. The device is thus completely en closed so as to protect it from dust and dirt.

In the embodiment illustrated in Figures 2, 3 and 4, the contactors are provided with an arcuate bearing surface 21 which bears against the outer flange of the cap 16. This bearing supports the pressue due to centrifugal force of the contactors so as to retain the same against flying off under such force. As the speed increases, the centrifugal force acting on the contactors increases. As the center of gravity of each contactor is displaced axially with respect to its bearing point on the flange of the cap 16, the centrifugal force will causesuch contact to tip as illustrated in Figures 3 and 4. Such tipping will be resisted by the pressure of the spring 9. The result is that the contactor pivots about the point 13 until the contact face 14 moves into engagement with the commutator. After such engagement the tipping continues while the contactor rolls on the commutator along its face 14. This movement is arrested when the retainer 7 comes into engagement with the cap 16 as shown in Figure 4.

In the embodiment illustrated in Figures 5, 6 and 7, the recess 15 is shaped in such a way as to provide a sharp pointat the pivot 13. This point is engaged in the flange of a supporting or retaining cup 22, fixed relatively to the shaft, which takes the pressure of centrifugal force. The tipping of the contactor takes place about this pivot point 13 in a manner similar to that described for Figures 2, 3 and 4. In this case, however, the point 13 slides outwardly along the flange of the cup 22 as the movement progresses. on the commutator along its face 14.

It will be seen, therefore, that in accordance with this invention a short circuiting device is provided which is adapted to make contact with the commutator at one point A, Figures 3 and 6, and then rolls to another point B, Figurestand 7. The point for maintaining the circuit is, therefore, different from the point at which the circuit is made or broken so that pitting or corrosion of the contact surfaces is avoided. The point for maintaining contact is, therefore, kept clean and smooth and in good condition for maintaining a low resistance contact. Moreover, this end is accomplished by a rolling contact rather than a sliding contact. A sliding contact is undesirable in a case like this for the reason that as soon as the make or break portion of the surface be comes rough by the corrosive action of the arc, the sliding friction is'increased often to a very great extent. Accordingly, since the centrifugal force is usually depended upon In this case also the contactor rollsto overcome the friction of these sliding surfaces, such roughening greatly increases that friction and renders the device unreliable in its operation.

The forces upon which the action of this device depends are illustrated diagrammatically in Figures 5,6 and 7. A similar arrangement of forces applies also to Figures 2, 3 and 4; The center of gravity of the contactor is approximately at the point X. The centrifugal force acts through this point in the direction indicated by the arrow F. The arrow G represents the reaction of the cup 22 against the pressure of the contactor. In the case of Figures 2, 3 and '4, this force is exerted by the outer flange of the cap 16. These two forces are displaced from one 'another'by a distance D represented by a dotted line in Figures 5, 6 and 7. These two forces represent a couple acting at a radius D to rotate the contactor. This couple is resisted by another couple composed of the force exerted by the retainer 7 upon the contactor and represented by the arrow R. The reaction against the pressure It is represented by the arrow S. The forces R and S'constitute a restraining or retaining couple acting at a radius represented by the distance between these two arrows.

Now, by reference to Figures 5, 6 and 7 it will be seen that as the cont-actor rotates about the pivot 13, the center of gravity X moves away from the commutator and away from the pivot 13, in an axial direction. This tends to increase the radius of the con ple tending to rotate the contactor. At the same time such rotation has the effect of moving the center of gravity X radially outwardly so as to increase its distance from the center of rotation so as to also increase its centrifugal force. It will be clear, therefore, that as the tipping movement progresses, the tipping couple increases due to both an increase in its radius and an increase in the intensity of the forces consututing the couple. On the other hand, the restraining couple, composed of the forces R and S, is'not increased but may, infact, be decreased. The spring 9 suflers but slight compression during this movement. Accordingly the increase in its pressure will be slight. At the same time the distance between the points of action of the'forces R and S is decreased as the tipping action progresses. Accordingly, this rest-raining couple will increase very little, ifany, and may actually decrease. It will be clear, there'- fore, that the moving effort of the centrifugal force of each contactor will increase as the movement of the contactor progresses ata greater rate than any increase in the retarding effort oft-he opposing couple.

The result of this arrangement is that as soon as the critical speed of rotation is reached, the contactors will begin to tip. Since their movement is a plain pivot action having little, if any frictional retardation, such tipping will begin always at the same speed. As soon as the tipping movement begins, the tippin effort is greatly increased over the retarding effort and consequently the movement is accelerated and the contactors tipped to their final osition with a quick sna ping movement. his is a very desirable e ect in a motor of this type as it makes quick contact so as to cut down the arcing at the contacting points. In addition to this, it renders the device positive and certain in its action. This together with the fact that the contactor rolls on the commutator insures that the contacting surfaces will always be clean and smooth and the action of the device always the same.

It is obvious that various changes may be made in details of construction without departing from the spirit of this invention; it is, therefore, to be understood that this invention is not to be limited to the specific details shown and described.

Having thus described the invention, what is claimed is 1. In an alternating current motor having a commutator, means for short-circuiting the commutator, comprising, a movable contactor support having an outwardly extending flange, a series of movable contactors adapted for rolling contact with the commutator and peripherally arranged on said support adjacent said flange, fixed means engaging said contactors adapted to retain said contactors against radial movement at the point of engagement but permitting pivotal movement thereof, and means for tensioning said support adapted to cause said support flange to bear upon said contactors.

2. In an alternating current motor having a commutator, means for short-circuiting the commutator, comprising, a movable contactor support having an outwardly extending flange, a series of movable contactors adapted for rolling contact with the commutator and peripherally arranged on said support adjacent to and engaging said flange, a fixed flanged retainer, means on said contactors adapted for pivotal engagement with the flange of said retainer, and means for tensioning said support adapted to cause said support flange to bear upon said contactors.

3. In an alternating current motor having a commutator, means for shortcircuiting the commutator, comprising, a movable contactor support having an outwardly extend ing flange, a series of movable contactors peripherally arranged on said support adjacent said flange, fixed means adapted to retain said contactors against radial movement but permitting pivotal movement thereof, means for tensioning said support adapted to cause said support flange to bear upon said contactors, and a cover enclosing said support and said contactors.

4. In an alternating current motor having a commutator, means for short-circuiting the commutator comprising, a contactor support, a series of contactors each having a. pivot portion adapted to engage a retainer, a 'weighted portion radially within said pivot portion, and a contact face radially without said pivot portion adapted for rolling contact with the commutator, means for retaining said contactors at their pivot portions adapted to restrain radial movement but to permit pivotal movement thereof, and means for yieldingly restraining pivotal movement of said contactors.

5. In an alternating current motor having a commutator, means for short-circuiting the commutator comprising, a contactor support, a series of contactors each having a pivot portion adapted to engage a retainer, a weighted portion radially within said pivot portion, and a contact face radially without said pivot portion adapted for rolling contact with the commutator, means for retaining said contactors at their pivot portions adapted to restrain radial movement but to permit pivotal movement thereof, and means for yieldingly restraining pivotal movement of said contactors whereby such pivotal movement causes said cont-act face to engage the commutator at one point thereof and subsequent movement of said contactor causes the same to roll to another point of contact.

6. In an alternating current motor having a commutator, means for short-circuiting the commutator comprising, a contactor support, a series of contactors each having a pivot portion adapted to engage a retainer, a weighted portion radially within said pivot portion, and a contact face radially Without said pivot portion adapted for roll ing contact with a radial face of the commutator, means for retaining said contactors at their pivot portions adapted to restrain radial movement but to permit pivotal movement thereof, and means for yieldingly restraining pivotal movement of said contactors whereby such pivotal movement causes said contact face to engage the commutator at one point thereof and subsequent movement of said contactor causes the same to roll to another point of contact.

In testimony whereof I aflix my signature this 15th day of December, 1925.

EDWIN C. BALLMAN. 

